Multi-port tubes comprise elongated, generally flattened, tubular members having a plurality of at least partially separated fluid flow channels extending along their length. Such tubes are incorporated into radiators, condensers, and other heat exchange structures of the type employed in motor vehicles; heating, ventilation, and air conditioning systems; nuclear power plants; chemical processing facilities; and the like. In a typical application, a relatively large number of these multi-port tubes are stacked into an array and disposed so as to convey a liquid or gaseous heat exchange fluid through the multi-port interior. In most applications, the individual multi-port tubes are relatively small in cross section and have lengths ranging from several inches to several feet. Operational parameters of the heat exchange structures generally require that the multi-port tubes be capable of providing for the relatively unimpeded flow of fluid therethrough under high pressure conditions without leakage or bursting. In addition, the multi-port tubes must be of uniform and precise geometry so as to facilitate their assembly into precise arrays. Furthermore, given the very large number of such tubes incorporated into a typical heat exchanger application, it is also important that such tubes be relatively low in cost.
In many instances, extrusion processes have been employed in the prior art for the fabrication of multi-port tubes of this type. In an extrusion process, a molten metallic material is extruded under high pressure through a die to form the tubular structure. While extrusion processes are capable of providing elongated, seamless multi-port tubes, extrusion equipment is relatively expensive and costly to implement and control. Additionally, the fact that the extrusion process requires the use of molten metals limits the range of materials which may be practically utilized for the fabrication of the multi-port tubes; and, additives must be incorporated into the metal, either pre or post-heating, to insure that strength and corrosion resistance criteria are met.
In other approaches, conventional metal shaping techniques such as bending, roll forming, and the like are employed to fabricate the multi-port tubes. In a typical process of this type, a corrugated interior member of the tube is first formed by bending or the like and is subsequently wrapped or otherwise disposed within an exterior member which is then brazed or welded shut to form a closed tube encasing the corrugated insert which serves to define the multi-port interior. Systems for carrying out processes of this type are relatively complicated and expensive and occupy a large area of floor space. In addition, fabrication and handing of a separate insert portion complicates the assembly process and can compromise the integrity of the finished product. Published PCT application WO 2007/084984 of Zobel shows a multi-roller apparatus as configured to fabricate a flattened multi-port tube incorporating a separate corrugated insert.
In some instances, the prior art has looked to processes for the fabrication of multi-port heat exchanger tubes which do not require the use of a separate corrugated insert. U.S. Patent Application Publication 2005/0092476 shows a process in which a multi-port tube is fabricated from a single body of stamped sheet metal by a method in which separate halves of each port are defined in a series of stamping dies and subsequently folded into alignment and brazed together. This process requires precise alignment of the segments of the tube and relies upon formation of a large number of brazed joints to assure the integrity of the resultant structure. U.S. Pat. No. 5,441,106 discloses a roll forming process for the fabrication of multi-port heat exchanger tubes from a single piece of folded metallic material. As taught therein, the folded structure relies upon a brazed joint to maintain the tube in a closed structure. The tubing is formed in a multi-stage roll forming process which, in addition to being expensive and occupying a large amount of floor space, precludes the incorporation of mechanical locking features into the tube structure thereby conditioning the integrity of the tube solely upon the brazed joint. A similar roll forming process is shown in U.S. Pat. No. 7,657,986 wherein a series of roll forming dies progressively fold and shape a sheet of metallic material into a multi-port tubular structure.
Prior art extrusion and roll forming processes of the type discussed above all employ complicated, expensive, and large area apparatus. In addition, multi-port tube structures fabricated by methods of the prior art typically require extensive post-fabrication processing to assure that the thus produced tube structures meet the precise geometric requirements for the heat exchangers into which they will be fabricated. Such post-forming processing can contaminate the structures with metal shavings and the like further requiring additional cleaning steps. Also, processes such as extrusion and roll forming cannot easily add interior structures such as locking features, fluid flow control features, and the like to the multi-port tubes. In addition to all the foregoing, processes of the prior art are relatively slow. As will be explained hereinbelow, the present invention is directed to a high speed, relatively simple, compact and low cost rotary die forming system for fabricating multi-port tube structures.
Parts fabricated by the method of the present invention can incorporate internal locking and fluid control features. In addition, the parts are fabricated to precise geometric tolerances and do not require significant post fabrication processing. These and other advantages of the present invention will be apparent from the drawings, discussion, and description which follow.